Liquid crystal display (LCD) devices, which have been widely used for a television and a monitor because of advantages in displaying moving images and high contrast ratio, use the optical anisotropy and polarization properties of liquid crystal molecules of a liquid crystal layer to produce an image. Accordingly, an LCD device includes a liquid crystal panel having two substrates spaced apart and facing each other and a liquid crystal layer interposed between the two substrates and a backlight unit supplying light to the liquid crystal panel. An alignment direction of the liquid crystal molecules in the liquid crystal layer is controlled by an electric field generated between the two substrates and transmittance of the liquid crystal layer is changed according to the alignment direction.
Although twisted nematic (TN) mode LCD devices using a vertical electric field have advantages in resolution and ability of displaying moving images, the TN mode LCD devices using the vertical electric field have disadvantages in a viewing angle. Accordingly, in-plane switching (IPS) mode LCD devices using a horizontal electric field have been the subject of recent research.
FIG. 1 is a cross-sectional view showing a liquid crystal panel of an IPS mode LCD device according to the related art. In FIG. 1, the liquid crystal panel of the IPS mode LCD device includes first and second substrate 10 and 20 facing and spaced apart from each other and a liquid crystal layer 30 between the first and second substrates 10 and 20. First and second polarizing plates 40 and 50 are formed on outer surfaces of the first and second substrates 10 and 20, respectively. A transmission axis of the first polarizing plate 40 is orthogonal to a transmission axis of the second polarizing plate 50. A common electrode 12 and a pixel electrode 14 are formed on an inner surface of the first substrate 10. A horizontal electric field L is generated between the common electrode 12 and the pixel electrode 14, and liquid crystal molecules 31 in the liquid crystal layer 30 are aligned along the horizontal electric field L to be perpendicular to the common electrode 12 and the pixel electrode 14.
In the liquid crystal panel of the IPS mode LCD device, the common electrode 12 and the pixel electrode 14 are formed on the same substrate, i.e., the first substrate 10, and the horizontal electric field L is generated between the common electrode 12 and the pixel electrode 14. Since the liquid crystal molecules 31 are arranged along the horizontal electric field L parallel to the first and second substrates 10 and 20, the IPS mode LCD device has a relatively wide viewing angle.
When undesired charges causing static electricity are injected into the liquid crystal panel of the IPS mode LCD device, the horizontal electric field L and the alignment direction of the liquid crystal molecules 31 may be distorted. As a result, the liquid crystal panel of the IPS mode LCD device may be abnormally operated. Since the second substrate 20 of the liquid crystal panel of the IPS mode LCD device does not have a common electrode on the entire inner surface thereof, a transparent conductive metal layer 60 is formed between the outer surface of the second substrate 20 and the second polarizing plate 50 to prevent the static electricity. The transparent conductive metal layer 60 may be grounded by connection to a supporting means for the liquid crystal panel through a conductive tape (not shown). However, the production cost of the IPS mode LCD device increases due to a high material cost for the transparent conductive metal layer 60 and the fabrication process of the IPS mode LCD device is complicated due to the additional steps for the transparent conductive metal layer 60.